1. Technical Field
The present invention relates in general to head gimbal assemblies for data recording disk drives and, in particular, to an improved method for controlling pitch static attitude of sliders on integrated lead suspensions in head gimbal assemblies by improved processing during manufacturing thereof.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location having an air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive, by a cushion of air generated by the rotating disk. Within most HDDs, the magnetic read/write head transducer is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk. Each slider is attached to the free end of a suspension that in turn is cantilevered from the rigid arm of an actuator. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
The suspension of a conventional disk drive typically includes a relatively stiff load beam with a mount plate at the base end, which subsequently attaches to the actuator arm, and whose free end mounts a flexure that carries the slider and its read/write head transducer. Disposed between the mount plate and the functional end of the load beam is a ‘hinge’ that is compliant in the vertical bending direction (normal to the disk surface). The hinge enables the load beam to suspend and load the slider and the read/write head toward the spinning disk surface. It is then the job of the flexure to provide gimbaled support for the slider so that the read/write head can pitch and roll in order to adjust its orientation for unavoidable disk surface run out or flatness variations.
The flexure in an integrated lead suspension is generally made out of a laminated multi-layer material. Typically, it consists of a conductor layer (like copper), a di-electric layer (like polyimide), and a support layer (like stainless steel). The electrical lead lines are etched into the conductor layer, while the polyimide layer serves as the insulator from the underlying steel support layer. The steel support layer is also patterned to provide strength and gimbaling characteristics to the flexure. The conducting leads, called traces, which electrically connect the head transducer to the read/write electronics, are often routed on both sides of the suspension, especially in the gimbal region. Normally the traces consist of copper conductor with polyimide dielectric layer but no support stainless steel layer and only provide the electrical function. The mechanical function is provided by the flexure legs (stainless steel only), which normally run adjacent to the traces.
The static attitude of the slider is defined by the angular position of the slider ABS with respect to the mounting platform and is specified by design in conjunction with a specific ABS, so that the slider can maintain an optimal flying height for the transducer thereon to read and/or write data on to the recording surface of the disk. To counter the airlift pressure exerted on the slider during disk drive operation, a pre-determined load is applied through a load point on the suspension to a precise load point on the slider. The slider flies above the disk at a height established by the equilibrium of the load on the load point and the lift force of the air bearing. The load of the suspension together with static attitude, control and maintain the optimal flying height of the slider.
The pitch static attitude in a suspension is produced to a desired value by forming the flexure legs, and then adjusting by mechanical/thermal methods. Since, the traces are an integral part of the flexure in an integrated lead suspension, joined to the flexure legs near the transducer bonding area in the front and near the back (leading edge) of the slider in the back, the traces provide resistance to the deformation of flexure leg and deflection of flexure tongue by an opposing force. Hence a significantly higher force is needed to plastically deform the flexure legs to obtain a desired pitch angle that also includes the overcoming the opposite forces produced by the traces. This process leaves residual stresses in the traces and the traces do not remain in the same plane as that of the rest of the flexure. One way to confirm the existence of stress in the traces is to cut the traces or subject the suspension to thermal processes. The stress is relieved by either process and as a result the pitch angle is increased.
This is an inherent problem of the integrated lead suspension. Once the suspension is manufactured by the supplier with formed flexure legs and adjustment to achieve desired pitch angle, it comes with variable amount of stress in the conductive traces. A part or all of the stress is likely to be relieved if and when the said suspension is subjected to a thermal process, thereby changing the pitch static attitude of the suspension or head gimbal assembly.
To successfully achieve file performance, the read/write head must fly steadily at a given fly height over the disk with minimal variations. Since the variations in fly height are dependent on the various sensitivities of the fly height to the process parameters as well as the variability of the parameters, a state-of-the-art air bearing surface (ABS) design and tight process control are mandatory to minimize such variations. Pitch static attitude and variations significantly affect the fly height. Moreover, a very low or negative pitch static attitude can cause disk damage and a very high pitch angle can promote a bi-stable behavior in fly height.
Thus, an improved method and system for controlling process parameters, such as pitch static attitude, of sliders on integrated lead suspensions in head gimbal assemblies for disk drives during the manufacturing thereof is needed.